diff --git a/lib/exposure/exposure.js b/lib/exposure/exposure.js
index 1023552..aa6a143 100644
--- a/lib/exposure/exposure.js
+++ b/lib/exposure/exposure.js
@@ -53,20 +53,19 @@ export default class Exposure {
         this.initCountMethod();
     }
 
-    _validateAndClean() {
-        if (typeof(this.config) === 'function') {
-            const firewall = this.config;
-            this.config = {firewall};
+    _validateAndClean(config) {
+        if (typeof(config) === 'function') {
+            const firewall = config;
+            config = {firewall};
+        }
+        config = ExposureConfigSchema.clean(config);
+        ExposureConfigSchema.validate(config);
+
+        if (config && config.body) {
+            ExposureConfigSchema.validateBody(this.collection, config.body);
         }
 
-        this.config = ExposureConfigSchema.clean(this.config);
-        ExposureConfigSchema.validate(this.config);
-        
-        if (this.config && this.config.body) {
-            ExposureConfigSchema.validateBody(this.collection, this.config.body);
-        }
-
-        return _.extend({}, Exposure.getConfig(), this.config);
+        return _.extend({}, Exposure.getConfig(), config);
     }
 
     /**
@@ -207,4 +206,4 @@ export default class Exposure {
             return findOne(filters, options);
         }
     }
-};
\ No newline at end of file
+};